Pregnant women are at risk for folic acid deficiency. While overt megaloblastic anemia is uncommon in these women, the marginal deficiency observed may have an adverse effect on the growth and folic acid status of the newborn. The major objective of this research is to find out what effects a marginal deficiency of folic acid deficiency during human pregnancy, the cebus monkey (Cebus albifrons) will be used as a primate animal model for this research. Female monkeys will be fed semipurified diets containing low, marginal, modeate and high levels of folic acid during the gestation and lactation periods. Blood samples will be obtained beiweekly for analysis of plasma and red blood cell folate and for determining the hematologic parameters including any development of megaloblastic anemia. Eight-hour urine collections will be made for analysis of formiminoglutamic acid excretion, a biochemical indicator of folic acid deficiency. Bone marrow and live biopsies will be performed to determine bone marrow cytology and total folate concentration, respectively. Blood samples will be taken from infant monkeys shortly after birth and at four weeks of age for folate analysis and complete hematology. Folic acid in plasma, whole blood, liver, experimental diet and dam's milk will be analyzed by microbiological assay. The deoxyuridine suppression test in lymphocytes will be used to assess folate coenzyme function in DNA synthesis. The data obtained will be used to compare the sequential appearance of any clinical or biochemical signs of folic acid deficiency in the mother and the neonate, to compare the folate status of the mother with that in the infant and to estimate the requirement for folic acid for pregnancy and lactation in the cebus monkey and relate this requirement qualitatively to the nonpregnant requirement and the growth rate of the infant.